1. Field of the Invention
This invention relates in general to chart recorders, and more particularly, to a data plotter for use therein.
2. Description of the Prior Art
Well-known multiple channel strip chart recorders have been provided for recording time-variant analog data by means of ink or heat pens in contact with a moving paper strip or other recording medium. Such recorders are frequently employed to record analog data comprising time-variant scalar or magnitude components of vector data signals having both magnitude and direction. Along with the recording of such scalar data, it is frequently desirable to simultaneously plot or record vector information and other data derived from the scalar data as an aid in the interpretation of their analog traces.
For example, in the clinical interpretation of electrocardiographic information, which includes analog traces of time-variant scalar components of vector heart potentials or voltages, it is a significant aid to diagnostic accuracy to observe plots of the voltage vectors and other data derived from the scalar data components along with the standard scalar electrocardiogram. In the cardiac cycle, the heart generates time-variant voltages or potentials which are vector quantities having both magnitude and direction. During each heart cycle, these voltages sweep through a three-dimensional pathway called a vector loop, initially increasing from zero value while being directed toward one side of the heart, then reaching a maximum, and then decreasing back to zero value while directed toward the opposite side of the heart. A standard electrocardiogram separately records along three mutually perpendicular axes only the scalar components or magnitudes of these three-dimensional time-variant vector potentials. However, observation of the planar vector loops is extremely helpful in the interpretation of the standard electrocardiogram data. An analysis of the heart vector potentials and the interpretation of their vector loops can be found in Clinical Vectorcardiography, by Chou, Helm and Kaplan, published by Grune and Stratton of New York and London in 1974.
Although available, instrumentation for recording or displaying such vector loops and other derived data is extremely expensive and cumbersome to operate in a clinical setting. Such equipment typically involves the photography of vector loops while they are being displayed on a cathode ray screen, and requires an expensive camera, a hooded cathode ray tube, electronic amplifiers and a power supply. Furthermore, it is difficult for the operator, while viewing the screen through the hood, to correlate the briefly displayed vector loops with the conventional electrocardiogram tracings.
Although chart recorders such as those disclosed in U.S. Letters Pat. No. 3,840,878, which issued Oct. 8, 1974 to Houston and Wilson, have been provided with print heads movable across the chart paper for recording digital characters and data, applicants are unaware of any self-contained chart recorder having a stationary printing device capable of printing or plotting data derived or computed from sampled input data.